1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by using a perpendicular magnetic recording system and to a method of manufacturing such a magnetic head.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction orthogonal to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
Like magnetic heads for longitudinal magnetic recording, magnetic heads for perpendicular magnetic recording typically used have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head comprises a magnetic pole layer that produces a magnetic field in the direction orthogonal to the surface of the recording medium. The pole layer incorporates a track width defining portion and a wide portion, for example. The track width defining portion has an end located in a medium facing surface that faces toward the recording medium. The wide portion is coupled to the other end of the track width defining portion and has a width greater than the width of the track width defining portion. The track width defining portion has a nearly uniform width.
For the perpendicular magnetic recording system, it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in writing characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, if the track width is reduced, the writing characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, are reduced. It is therefore required to achieve better writing characteristics as the track width is reduced. Here, the length of the track width defining portion orthogonal to the medium facing surface is called a neck height. The smaller the neck height, the better is the overwrite property.
A magnetic head used for a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the above-mentioned medium facing surface. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider slightly flies over the surface of the recording medium by means of the airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt called a skew of the magnetic head is created with respect to the tangent of the circular track, in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system that exhibits a better capability of writing on a recording medium than the longitudinal magnetic recording system, in particular, if the above-mentioned skew is created, problems arise, such as a phenomenon in which data stored on an adjacent track is erased when data is written on a specific track (that is hereinafter called adjacent track erasing) or unwanted writing is performed between adjacent two tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between adjacent two tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
A technique is known for preventing the problems resulting from the skew as described above, as disclosed in the Published U.S. Patent Application No. 2003/0151850A1, the Published Unexamined Japanese Patent Application 2003-203311, and the U.S. Pat. No. 6,504,675B1, for example. According to this technique, the end face of the track width defining portion located in the medium facing surface is made to have a shape in which the side located backward in the direction of travel of the recording medium (that is, the side located on the air-inflow-end side of the slider) is shorter than the opposite side. Typically, in the medium facing surface of a magnetic head, the end farther from the substrate is located forward in the direction of travel of the recording medium (that is, on the air-outflow-end side of the slider). Therefore, the above-mentioned shape of the end face of the track width defining portion located in the medium facing surface is such a shape that the side closer to the substrate is shorter than the side farther from the substrate.
As a magnetic head for perpendicular magnetic recording, a magnetic head comprising a pole layer and a shield is known, as disclosed in the U.S. Pat. No. 4,656,546, for example. In the medium facing surface of this magnetic head, an end face of the shield is located forward of an end face of the pole layer along the direction of travel of the recording medium with a specific small space. Such a magnetic head will be hereinafter called a shield-type head. In the shield-type head the shield prevents a magnetic flux from reaching the recording medium, the flux being generated from the end face of the pole layer and extending in directions except the direction orthogonal to the surface of the recording medium. The shield-type head achieves a further improvement in linear recording density.
The U.S. Pat. No. 4,672,493 discloses a magnetic head having a structure in which magnetic layers are provided forward and backward, respectively, in the direction of travel of the recording medium with respect to a middle magnetic layer to be the pole layer, and coils are disposed between the middle magnetic layer and the forward magnetic layer, and between the middle magnetic layer and the backward magnetic layer, respectively. This magnetic head is capable of increasing components orthogonal to the surface of the recording medium among components of the magnetic field generated from the medium-facing-surface-side end of the middle magnetic layer.
Consideration will now be given to a method of forming a pole layer that has a track width defining portion with an end face located in the medium facing surface and having a shape in which a side closer to the substrate is shorter than a side farther from the substrate as described above. It is frame plating that has been often used in prior art for forming such a pole layer. Reference is now made to FIG. 58 to FIG. 61 to describe an example of method of forming the pole layer by frame plating. FIG. 58 to FIG. 61 each illustrate a cross section of the track width defining portion of the pole layer and a neighborhood thereof, the cross section being parallel to the medium facing surface.
FIG. 58 illustrates a step of the method of forming the pole layer mentioned above. In this step, first, an electrode film 202 is formed on an insulating layer 201 to be a base of the pole layer. The insulating layer 201 is made of alumina (Al2O3), for example. Next, a photoresist layer is formed on the electrode film 202. The photoresist layer is then patterned to form a frame 203 having a groove whose shape corresponds to the pole layer. Next, plating is performed by feeding a current to the electrode film 202 to form the pole layer 204 in the groove. At the same time, an unwanted plating layer 205 is formed outside the frame 203.
FIG. 59 illustrates the following step. In the step, first, the frame 203 is removed. Next, a portion of the electrode film 202 that was located below the frame 203 is removed by ion beam etching, for example. At the same time, a portion of the insulating layer 201 that was located below the portion of the electrode film 202 removed is etched, too.
FIG. 60 illustrates the following step. In the step, first, the unwanted plating layer 205 and a portion of the electrode film 202 located below the plating layer 205 are removed by wet etching, for example. Next, an insulating layer 206 made of alumina, for example, is formed to cover the pole layer 204. The insulating layer 206 is made to have a thickness equal to the total thickness of the pole layer 204 and the electrode film 202 as desired. Next, a stopper film 207 is formed on the insulating layer 206 except a region near the pole layer 204. Next, an insulating layer 208 made of alumina, for example, is formed on the entire top surface of the layered structure.
Next, as shown in FIG. 61, the insulating layer 208 and the pole layer 204 are polished by chemical mechanical polishing (hereinafter referred to as CMP), for example. This polishing is stopped when the stopper film 207 is exposed. Through the polishing, the top surface of the pole layer 204 is flattened, and the thickness of the pole layer 204 is controlled to have a desired value.
Problems of the method of forming the pole layer illustrated in FIG. 58 to FIG. 61 will now be described. As shown in FIG. 61, when the polishing of the insulating layer 208 and the pole layer 204 is completed, there is a difference ‘d’ in level between the top surface of the stopper film 207 and the top surface of the pole layer 204 such that the top surface of the pole layer 204 is lower. The greater the distance D between the stopper film 207 and the pole layer 204 (See FIG. 60), the greater is the difference ‘d’ in level. The difference ‘d’ in level increases as the amount of polishing the insulating layer 208 and the pole layer 204 increases. The distance D is about 10 to 15 μm. Here, the distance D is 15 μm by way of example, and the initial thickness of the insulating layer 208 is 0.6 μm. In this case, the difference ‘d’ in level is about 0.15 μm. As thus described, if the difference ‘d’ in level is created, there arises a problem that the thickness of the pole layer 204 falls out of a desired value.
The end face of the track width defining portion located in the medium facing surface has such a shape that the side closer to the substrate is shorter than the side farther from the substrate, as described above. The side farther from the substrate has a length equal to the track width. Here, if the thickness of the pole layer 204 falls out of a desired value as described above, there arises a problem that the track width defined by the above-mentioned length of the side farther from the substrate falls out of a desired value.
Through the method of forming the pole layer illustrated in FIG. 58 to FIG. 61, it is impossible to measure with accuracy the shape of the end face of the track width defining portion located in the medium facing surface in the course of manufacturing process of the magnetic head. Therefore, even if the thickness of the pole layer 204 or the track width falls out of a desired value as described above, it is impossible to recognize that until the magnetic head is completed, and the efficiency in manufacturing the magnetic head is reduced.
The Published U.S. Patent Application No. 2003/0151850A1 discloses a method in which a groove having a shape corresponding to the pole layer is formed in an inorganic insulating film, and the pole layer is formed in the groove by plating or sputtering. In this method the width of the pole layer, that is, the track width, is defined by the width of the groove formed in the inorganic insulating film. In addition, the Published U.S. Patent Application No. 2003/0151850A1 discloses that, when the pole layer is formed in the groove by plating, a stopper film used for CMP may be formed after the plating base film is formed. However, this publication does not disclose any range in which the stopper film for CMP is formed.